Once again, I’ve gone back to my correspondence files to select various reader inquiries related to resilient installation concerns, problems and procedures. Hopefully, the 10 questions I answer here will someday aid you if you encounter similar issues during the course of doing business.

Q: Why does it seem that there are so many moisture-related problems with flooring installations in surgery rooms and schools?
I’ve seen moisture-related problems in an operating room where no problems were evident in the corridors outside. The reason? The temperature and humidity levels in the operating room are different than those in the corridor. Because the driving force of moisture vapor movement is temperature and humidity, the moisture movement is greater in the operating room. Often, in a school environment, temperature and humidity are allowed to fluctuate in the structure. When school is in session, the temperature and humidity controls are activated. But whenever the school is not being used -- during nights, weekends and holidays -- the temperature and humidity controls are turned down to conserve energy. The effect is fluctuation in moisture vapor movement.

Q: How thick does a cementitious underlayment have to be to serve as a barrier coat that prevents discoloration due to the adhesive’s effect on vinyl-backed sheet goods?
Many installers feel that a thin skimcoat will suffice as a barrier. Not true! A barrier coat must be just that -- a barrier. If a barrier coat is to be effective in the prevention of plasticizer discoloration, it must be a minimum of 1/16-inch thick. To render the skim coat porous, the layer would have to be 1/8-inch thick.

Q: Does the open time of an adhesive change when it’s applied over an embossing leveler?
Yes. Generally speaking, the open time and working time of an adhesive is cut in half. Because of its absorbency, the adhesive will dry faster and the working time will be shortened by as much as 50%.

Q: Just how freeze-thaw stable are multi-purpose adhesives?
Many adhesives are billed as “freeze-thaw stable.” Some are limited to a certain sub-freezing level, and some are limited to the number of times they can be frozen before performance is negatively affected. It’s been my experience that each time an adhesive is subjected to freezing conditions, the character of the adhesive is altered -- and never for the better. To maintain the quality of adhesive you are using, your best bet would be to protect the product from freezing conditions.

Q: In situations where a concrete slab has undergone a moisture-remediation treatment, the slab “appears” to be non-porous. In fact, does the cementitious underlayment coat change the porosity of the slab?
A concrete slab that has had a moisture vapor-control system applied to its surface fools many flooring installers. Any such moisture-control system renders the slab non-porous. In general, the thicker the cementitious underlayment is applied, the more porosity the surface of the slab will have. Consequently, the thinner the underlayment coat, the less porosity the slab will have.

Q: How do you determine what the heat setting to use on a heat gun?
Many variables are involved in determining the heat setting on a heat gun. Here are seven of them:
1. The settings vary from heat gun to heat gun, and from manufacturer to manufacturer.
2. The quality of the power source, and the length and size of the power cord you intend to use, affects the gun’s heat output.
3. The temperature of the floor also affects the choice of heat setting.
4. What type of material is used in the substrate? Wood tends to be a little warmer than concrete. You would want to make heat adjustments accordingly.
5. What type of material are you going to be welding? Rubber, vinyl and linoleum all require different heat settings.
6. What type of weld rod are you using? Round, patterned half-round or thermo-plastic (linoleum) rods each have different heating requirements.
7. How fast are you going to move through in the welding process? Some installers work faster than others do, so the heat setting needs to vary according to the speed at which you weld.

Q: I performed a large commercial installation in which the seams opened up after about two years. A seam sealer was applied to the seam, but it has started to let go in places. What do you think caused this problem?
There are several possible reasons for the seam failure. The most common causes are: the seam edges of the material were contaminated with adhesive; the seam sealer was topically applied; or the seams were sealed when the flooring material was cold.

Q: Will a crack-suppression unit perform as intended when resilient floors are installed over cracked concrete?
A lot depends upon the type of crack in the concrete and its cause. Very little movement in a concrete slab is capable of creating a crack that will show through a resilient floor. I believe it’s highly doubtful that a crack-suppression unit would work as you intend, primarily due to the effect of thermo movement in concrete.

Q: A customer of mine has a linoleum floor that yellowed beneath an area rug. Is there something in the area rug that would cause this yellowing?
No, I think you will find that the material not covered by the rug has lightened as a result of exposure to natural light. Linoleum is known to develop a yellowish cast as the linseed oil in the product undergoes the curing process.
I would advise your customer to remove the rug for a couple of weeks and expose the area formerly covered by it to natural light. You will find the similar color variations with some types of wood floors, although the exposed areas tend to darken more than those covered by rugs and furniture.

Q: I’ve been told that many wood underlayment manufacturers are recommending tighter nailing patterns for underlayment installation. What is the reason for this?
Yes, many underlayment manufacturers have tightened up their fastening requirements in an effort to help eliminate some of the joint show-through problems that arise in certain flooring installations.
While acclimation is still extremely important to the ultimate success or failure of an underlayment installation, the fastening pattern is of equally critical. Fastener spacing along the perimeter of ¼-inch panels has been reduced from 4 inches to as little as 2 inches. The accepted fastener placement relative to the panel edges remains within 3/8 inch of the joint. The spacing in the field of the panel has been tightened from 6 inches to as little as 4 inches. This translates to a few more fasteners and, in theory, fewer problems.

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